﻿Yol. 66.~] VOLCANO OF MATAVANU IX SAVAII. 633 



watched the formation of ordinary corded lava on Vesuvius by a 

 similar process of budding. When the hot lava of the interior has 

 got vent and formed a pool, a soft scum forms on the surface, 

 which is pushed forward by the fluid lava moving beneath, and 

 is raised into a wrinkle or cord, then others are formed in the same 

 way, until the surface is entirely solidified into a succession of 

 cords (PI. XLVIII, fig. 1). The same sort of process can often be 

 watched on the surface of a slowly moving river when rubbish 

 floating on the surface is stopped behind a log of wood. Here it 

 was different : there was no trace of the formation of wrinkles and 

 cords. The whole surface seemed to be chilled at once, as the 

 waves rolled on and off, and examination of cooled specimens 

 between high and low water-mark at the edge of the lava in the 

 lagoon confirmed this. The surface at and below the water-level 

 was roughly granular, like that of air-chilled bombs such as I have 

 seen on Stromboli and Haleakala, while higher up the ordinary 

 corded or pahoehoe structure was seen (PI. LII). I was vividly 

 reminded of a section that I have seen at Aci Castello in Sicily. 



Before the eruption a small river came down from the mountains, 

 passed through the villages of Patamea and Samalaeulu, and fell 

 into the sea at Sataputu. Both the higher and the lower reaches 

 of the river have been covered over and filled up with lava, leaving 

 the channel at Patamea and Samalaeulu unobstructed, but usually 

 empty. The rain, which falls on the former gathering-ground, is 

 soaked up by the lava and possibly percolates elsewhere, so that 

 scarcely any water now comes down the channel except in very 

 heavy rain-storms, which have only occurred once or twice since 

 the eruption. On one such occasion the water could not get away 

 owing to the obstruction near the old mouth, and the country 

 round was flooded. The empty channel is a good example of a 

 water-eroded gorge cut in geologically recent beds of lava, and 

 shows the usual water-holes, as also small falls in its bed. At one 

 place where I saw it, it was nearly 30 feet deep and not much 

 wider. At others it was perhaps 3 or 4 times as wide. 



The Destruction of Buildings. 



The native houses in the villages destroyed consisted merely of 

 thatched roofs supported on wooden poles. The churches of 

 Saleaula and Sataputu were, however, substantial stone buildings, 



Clements, J. M., Monogr. U.S. Geol. Surv. xxxvi (1899) p. 124, thinks 

 that pilow-lava is a form, of aa, not pahoehoe. The aa referred to is 

 not the common scoriaceous form, but one described by Dana as above. 



Having now seen the actual formation of all three — aa, pahoehoe, and 

 pillow-lava, I am satisfied that the scoriaceous form of aa is produced by 

 watery vapour expanding from inside the pores of the lava ; pahoehoe from 

 the slow cooling of lava containing little vapour; and pillow-lava (at any rate 

 one form) from the chilling action of water on the surface before it has time 

 to assume the corded structure of pahoehoe. I have not seen the formation 

 of aa as described by Dana. 



